Normal and abnormal leukocyte function (chemotactic and phagocytic) will be studied. Emphasis will be placed on the role of complement-derived and lymphocyte-derived mediators that have an ability to alter cell movement. Interactions of mediators with leukocytes will be assessed. The ability to alter leukocyte function by pharmacological manipulation will be studied. Finally, abnormal metabolism of complement in nephritic syndromes will be assessed, as will cultures of synovial cells from patients with rheumatoid arthritis.